Hydraulic valve lifters (also known as hydraulic lash adjusters “HLAs” or hydraulic tappets) are used to maintain a valve clearance in internal combustion engines. Maintaining valve clearance is important as it reduces noise and allows an engine to run more efficiently. Hydraulic valve lifters function by transferring energy from the actuating cam lobe to the pushrod and ultimately the rocker arm via hydraulic oil in a pressure chamber. The hydraulic valve lifter changes length by varying the oil level in the system. Oil is added to the hydraulic valve lifter to elongate the system and oil is allowed to escape to shorten the system. By changing length, the lifter maintains contact between the elements and thus eliminates any lash or gaps that would result in unwanted noise.
When the valve train includes hydraulic valve lifters and pushrods it is possible to supply oil from the rocker arm or rocker arm shaft to the hydraulic valve lifters through the pushrods. This allows the oil inside the pushrod to form part of the low pressure reservoir and decreases the size of the lower pressure chamber in the hydraulic valve lifters allowing for a more compact assembly. In this arrangement, oil can leak from the hydraulic valve lifters and the pushrod. When this occurs, the hydraulic valve lifters fail to maintain a desirable valve clearance, which may result in undesirable valve operation such as lash and noise during valve operation. This problem is aggravated when the hydraulic valve lifters and pushrods are oriented in near horizontal arrangements as there is greater opportunity for oil to drain from the hydraulic valve lifters when they are not in operation. Therefore, there is need for improvement in the art.